Recent N. Texas quakes near to injection wells

Updated 8:30 pm, Monday, August 6, 2012

Most recent earthquakes in North Texas happened close to injection wells used to dispose of wastewater from oil and gas drilling in the region, according to new research.

A two-year study by the University of Texas at Austin also found that the relatively minor temblors happened more often than indicated in previous investigations.

The UT study, published this week in the journal Proceedings of the National Academy of Sciences, is the latest to suggest a link between drilling and seismic activity.

The report doesn't find any direct link between hydraulic fracturing and earthquakes. But it adds to concerns that injection wells, where wastewater from fracking and production is pumped back into the ground, can cause increased seismic activity.

“You can't prove that any one earthquake was caused by an injection well,” said Cliff Frohlich, the University of Texas researcher who conducted the study. “But it's obvious that wells are enhancing the probability that earthquakes will occur.”

Although Frohlich's research focused on the Barnett Shale in North Texas, recent rumblings in the Eagle Ford formation also have drawn attention. A record-setting magnitude 4.8 earthquake rattled Central and South Texas last October, followed by a magnitude 3.3 quake in November. Neither was linked with injection wells or drilling in the region, but they stoked fears of fracturing-tied tremors.

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Frohlich has said he would like to study seismic activity in the Eagle Ford Shale in South Texas for comparison.

A U.S. Geological Survey report released earlier this year found that an increase in small temblors throughout the Midwest coincides with the injection of drilling wastewater in deep disposal wells. An Ohio state agency concluded in March that a wastewater injection well was responsible for a dozen earthquakes in Youngstown last year. And in June, the National Research Council released a report concluding that while there is a low risk of earthquakes directly tied to oil and gas drilling techniques, underground wastewater injections pose a higher risk of triggering seismic activity.

Drilling companies have said they do not believe earthquakes are linked to injection wells.

The wells store wastewater from hydraulic fracturing, a drilling and well stimulation technique that involves pumping mixtures of water, sand and chemicals underground to release natural gas and oil trapped in dense rock formations.

Frohlich's research focused on seismic data from the Barnett Shale region from November 2009 to September 2011. He concluded that the most reliably pinpointed earthquakes occurring during that time were in eight groups, all located within two miles of one or more injection wells.

But his data also show disparities. In some cases where drillers rapidly disposed of wastewater underground, there were temblors nearby. But in other cases with similar circumstances, there were no resulting quakes.

Frohlich speculated the difference may be that wastewater injected in some wells reaches existing faults.

Some of the earthquakes were too small to feel on the surface, while others, as high as 2.5 in magnitude, still were too light to pose any real danger, the study said.

Ed Ireland, director of the Barnett Shale Energy Education Council, said any correlation between injection wells and seismic activity would need more study, noting that there are more than 50,000 injection wells in Texas and that most have had no problems reported.